(1) Field of the Invention
The present invention relates to an electro-oculography estimating device, an electro-oculography calculating method, an to eye-gaze tracking device, a wearable camera, a head-mounted display, and electronic eyeglasses.
(2) Description of the Related Art
Conventionally, an eye-gaze tracking technique using Electro-oculography (EOG) is well known. The technique is to detect an eye-gaze by measuring eye potential (electro-oculogram) generated by a positive charge in a cornea and a negative charge in a retina, using a plurality of electrodes attached around eyes. Unlike an eye-gaze tracking technique for capturing an image of an eyeball using a camera, this technique using EOG has such advantages as not interfering with vision, not being influenced by outside light, not depending on a shape and an opening state of the eye, and achieving low power consumption, and thus is expected to be applied to various devices.
However, while the conventional eye-gaze tracking technique using EOG performs linear approximation on a relationship between the gaze and EOG, EOG that is actually measured becomes more nonlinear when a gaze angle is larger. For this reason, the conventional eye-gaze tracking technique using EOG has low accuracy in gaze detection (gaze error 5° to 10°).
<Battery Model of Eyeballs>
Thus, Non-Patent Reference 1 discloses a nonlinear model of EOG. Non-Patent Reference 1 suggests a model (battery model) which assumes the cornea of an eyeball as a plus battery and the retina as a minus battery, and uses a battery rotation to resemble eyeball movement. When r and r′ represent distances from an electrode to the cornea center and the retina center, respectively, I is a current flowing from the retina to the cornea within the eyeball, and σ is conductivity around the eyeball, potential v generated at the electrode is calculated in accordance with (Expression 1) below:
                    (                  Expression          ⁢                                          ⁢          1                )                                                            v        =                              J                          4              ⁢              πσ                                ⁢                      (                                          1                                  r                  ⁢                                                                                                    -                              1                                  r                  ′                                                      )                                              [                  Math          ⁢                                          ⁢          1                ]            
This shows a possibility of evaluating EOG in a mathematical expression, and describes the method as effective for clinical application in the future (as an electrophysiological method for obtaining information from eye fundus that cannot be visually obtained, estimation of visual impairment, or the like).